Oelker, Julia; Auel, Holger; Janßen, Silke; Koppelmann, Rolf; Martin, Bettina (2025): Continuous optical chlorophyll-a and turbidity data along RV SONNE cruise SO308/2 [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.987943 (DOI registration in progress)

Underway optical chlorophyll-a and turbidity data were collected along the cruise track with Sea-Bird Scientific ECO FLNTU sensors installed within two autonomous measurement systems, called self-cleaning monitoring boxes (SMBs). The SMBs measure alternatingly. While one box is measuring, the other one is being cleaned. The boxes switched generally every 12 hours. The water inlet for the SMBs is at about 4 m below sea surface. Observed chlorophyll-a and turbidity data were both quality controlled. Analysis of the chlorophyll-a and turbidity data during parallel operation of the sensors in the two boxes showed significant differences between the sensors. The sensors were aligned resulting in consistent chlorophyll-a and turbidity time series. The corrected chlorophyll-a data was compared with reference chlorophyll-a from water samples collected with Niskin bottles of the CTD water sampler at 10 m depth and satellite data, the Globcolour CHL1 product. Since the first half of the time series shows 24 h period cycles which are likely connected to non-photochemical quenching which could not be separated from actual changes in biomass, the reference chlorophyll-a samples were not used for calibration. Roughly, high chlorophyll-a values were estimated to be at least a factor three too high. Details on all quality control steps and the comparison with satellite data can be found in the data processing report. It was out of the scope of the quality control to flag or correct non-photochemical quenching. The resulting data set contains the original data and corresponding quality flags achieved by the quality control algorithm as well as the corrected chlorophyll-a and turbidity data with corresponding quality flags. The data source is given through the name of the active SMB. The data set contains data during transit time and station work. We recommend to use ship's speed to filter for only transit data.